Asics Gel Hyperspeed 4 Review
Asics didn't update much this year with the release of the Hyperspeed 4, so just about everything mentioned in my Asics Gel Hyperspeed 3 review still applies. According to the stats they added .1 oz of weight to the shoe, but I doubt your feet will notice.
The Hyperspeed is still one of my top recommendations. It has a little more cushioning than some of the most extreme flats out there like the even lighter Asics Piranha's, but it maintains a low heel to toe raise difference (just 5mm) and a very light weight at 7.2oz. It's also kept a rubberized bottom which I highly prefer over the hard tack surface a lot of flats use, and the lack of any rigid arch support keeps the entire length of the shoe very flexible. The biggest downside is still the odd pattern Asics chose for the bottom of the shoe which seems to be designed to pickup pebbles. Once they're broken in the gap gets a little smaller so you pickup fewer, and they're usually easy enough to kick out, but it's still annoying that they'd keep those pebble pockets around at all.
Pros: Light (7.2 oz), Flexible, Low Heel to Toe Differential (5mm), Rubber Bottom for better wear & tear
Cons: It's a great midrange flat but if you're looking for pure speed (or hate ride-along rocks with a passion) it can be beat. There's slightly lighter, more flexible, and even lower heel to toe difference shoes out there like above mentioned Piranha. However if you're transitioning to training in flats, or looking for one of your first pairs, this could be just what you're looking for.